See Forum post: https://www.spigotmc.org/threads/translatablecomponent-doesnt-work-in-the-actionbar.370799/

The title says it all, basically

The following line of code reproduces the bug:

player.spigot().sendMessage(ChatMessageType.ACTION_BAR, new TranslatableComponent("block.minecraft.iron_ore"));

The text shown in the action bar is always the english translation of "iron ore", no matter what language the client uses, while

player.spigot().sendMessage(ChatMessageType.CHAT, new TranslatableComponent("block.minecraft.iron_ore"));

prints the right translation to the player's chat.

The Vanilla equivalent

/title @a actionbar {"translate":"block.minecraft.iron_ore"}

works just fine.

The minimal reproduction plugin executes these two lines, using a player interaction as a trigger (left/right click).

Set your game language to something other than english, join a server with the reproduction plugin, punch the air and enjoy the bug